Analyzing your own nitrox tanks

[autrichon gris]

Do you have to use Ratios sensors when replacing or can you use others?

You can use others (as far as i understood, never did it at that time).

 

[ZephyrNYC]

The air is the big, free tank that is always 20.9.

[EDITED so as not to confuse future readers:
I STAND CORRECTED. The FRACTION of oxygen, nitrogen, etc. is always the same. It's the PARTIAL PRESSURE of oxygen, nitrogen, etc. that changes with elevation.]

Not always. There are already 1 or more comments about humidity and temperature. Another factor is air pressure, which is dependent on elevation among other things. For example, a popular dive site in Utah is the Flaming Gorge Dam at 6045' ASL. If you were to calibrate your analyzer to the air at 20.9% [at sea level, THEN TRAVEL to a different elevation, 6045' ASL in this example], your analyzer would be inaccurate, as the effective O2 percentage at that altitude is around 16.6% [PPO2 of 0.166 atm].
[THEREFORE YOU MUST RECALIBRATE YOUR ANALYZER AT ELEVATION in order to get an accurate PPO2.]

 

[tursiops]

I for the life of me can't find cheap O2 sensors on AliExpress. Do you have any suggestions on what to search for?

I plan to use them to verify vs a good sensor (typically on test builds). Just hard to justify spending $100 on a spare sensor that I don't really need.

Seach for "oxygen sensor scuba" or "electrochemical sensor scuba"

 

[inquis]

Not always. There are already 1 or more comments about humidity and temperature. Another factor is air pressure, which is dependent on elevation among other things. For example, a popular dive site in Utah is the Flaming Gorge Dam at 6045' ASL. If you were to calibrate your analyzer to the air there at 20.9%, your analyzer would be inaccurate, as the effective O2 percentage at that altitude is around 16.6%.

No, the O2 fraction is still 20.9% (assuming humidity/temp don't shift it). It is the partial pressure of O2 that is 16.6 atm. You should get a reading of 20.9% on a correctly calibrated analyzer.

 

[TravisD]

No, the O2 fraction is still 20.9% (assuming humidity/temp don't shift it). It is the partial pressure of O2 that is 16.6 atm. You should get a reading of 20.9% on a correctly calibrated analyzer.

Isn't that the whole thing though? O2 sensors measure PPO2, not FO2.

 

[jborg]

Yes but what pressure is the nitrox from your tank at, when it hits the analyzer? I would guess very close to that of the ambient atmosphere, unless you have an unusual arrangement.

 

[inquis]

Isn't that the whole thing though? O2 sensors measure PPO2, not FO2.

Yes, and to come full circle, that is exactly why we calibrate the analyzer. That way we can read the fraction directly and configure the computer appropriately.

 

[BRT]

Not always. There are already 1 or more comments about humidity and temperature. Another factor is air pressure, which is dependent on elevation among other things. For example, a popular dive site in Utah is the Flaming Gorge Dam at 6045' ASL. If you were to calibrate your analyzer to the air there at 20.9%, your analyzer would be inaccurate, as the effective O2 percentage at that altitude is around 16.6%.

I already covered temperature and humidity. You will be hard pressed to find temperature and humidity conditions that will make a huge difference. So far as altitude, try using your small tank of 20.9% at 6000 feet and see where that gets you. The partial pressure is the same for the big free tank or the small tank you have brought along, assuming your small tank is filled with the correct mixture. The analyzer is still going to be set to 20.9 which is the percentage of oxygen in the air at sea level and on top of Everest. If your analyzer can be calibrated to whatever number you want to enter then you can adjust for altitude whether you are using atmospheric air or your test tank.

 

[OMyMyOHellYes]

If you were to calibrate your analyzer to the air there at 20.9%, your analyzer would be inaccurate, as the effective O2 percentage at that altitude is around 16.6%.

Hep me understand how the composition of atmospheric air suddenly INCREASES the concentration of N2 to 83.3% in Utah. Or is it the other trace gases that increase so dramatically?

 

[ZephyrNYC]

Hep me understand how the composition of atmospheric air suddenly INCREASES the concentration of N2 to 83.3% in Utah. Or is it the other trace gases that increase so dramatically?

I stand corrected. Please take a look at my updated comment.